The invention relates to electronic semiconductor devices, and, more particularly, to planarization methods useful in device fabrication.
The manufacturing process flow for semiconductor devices includes planarization steps which are designed to selectively remove surface features which protrude from the wafer surface. Such features may be a consequence of blanket depositions of dielectric or metal films onto wafers with etched surface patterns or of localized depositions of materials in areas defined by photolithography and etching.
A desired property of the planarization process is a control of the selectivity of the removal rate with regard to different materials, such as grown silicon dioxide, vapor phase deposited polysilicon, silicon nitride, borophospho silicate glass, and metals like aluminum, titanium, tungsten, copper, et cetera.
Chemical mechanical polishing (CMP) is a process that combines chemical etching with mechanical abrasion by using a polishing pad with a polishing slurry which contains suspended abrasive particles; see heuristic FIG. 4. The chemical aspects of the removal are controlled by the composition of the polishing slurry. For example, etch removal of SiO2 can be achieved by hydroxide or bifluoride additions resulting in high pH values.
The mechanical component of the removal process is controlled by the addition of abrasive powders. SiO2, A1203 and CeO powders are examples for such materials.
Besides slurry composition and feed rate, type and particle size of the abrasive additive, CMP process parameters include type and hardness of the polishing pad, applied pressure and plate rotational speed.
For a detailed presentation of the CMP process reference is made to Beyer et al., U.S. Pat. No. 4,944,836 and to the review article by Ali et al, Chemical-Mechanical Polishing of Interlayer Dielectric: A Review, Solid State Technology, October 1994, p.63. More recent activities are reflected in a publication by Wijekoon et al., Tungsten CMP Process Developed, Solid State Technology, April 1998, p.53-56, describing the development of a commercial CMP process for the formation of tungsten plugs.
The composition of slurries is formulated for the achievement of specific process objectives and additives are in use to enhance process characteristics. In one specific example, Farkas et al., U.S. Pat. No. 5,614,444 introduced a family of additives that enhance the selectivity in metal CMP. Those additives have both polar and apolar components, the polar component interacts with functional groups at the oxide surface and forms an interacted apolar passivation layer. The additives thus block or replace the surface functional groups so that the interaction between the wafer oxide surface and the slurry is reduced and the corrosion process impeded. The metal surface remains unaltered by the additive and the result is that process selectivity for the metal oxide removal rate is enhanced.
During the manufacture of silicon integrated circuits, CMP finds extensive applications in the Shallow Trench Isolation (STI) process to planarize uneven surfaces. Silica powder with tight particle size specifications is preferably selected as abrasive component for this CMP process because it produces smooth, scratch free surfaces. The STI process requires removal rate selectivity for nitride and oxide films. This selectivity is controlled by the pH value; increasing the pH value enhances the nitride/oxide selectivity. Raising the pH value by adding a hydroxide like KOH to the CMP slurry has the undesired side effect of accelerating the decomposition of silica particles. Ongoing particle size reduction is reflected in continually changing removal characteristics and in a short slurry lifetime.
The functionalization of a silica surface has been demonstrated in the past. For example, organic reactions applied to chromatography include: Bayer et al. Characterization of chemically modified silica gels by . . . and 13C Cross-Polarization and Magic Angle Spinning Nuclear Magnetic Resonance, J. of Chromatography, 264 (1983) 197-213, reacted several organo-silicon compounds in toluene at 80 C under argon with silica and studied the character and the strength of the chemical bonds. Wirth et al., Horizontal Polymerization of Mixed Trifunctional Silanes on Silica: A Potential Chromatographic Stationary Phase, Anal. Chem. 1992, 64 2783-2786, worked with nearly solid layers of alkyl chains with CI3Si-R functionality. Some layers survived boiling in concentrated nitric acid for 25 minutes. Kirkland et al. Reversed Phase HPLC and Retention Characteristics of Conformationally Different Bonded Alkyl Stationary Phases, J. of Chromatographic Science, Vol.32, November 1994, p. 473-479, showed that some sterically protected dimethyl-C18 films show stability against hydrolysis in solutions with pH values as high as 9. Karch et al. xe2x80x9cPreparation and Properties of Reversed Phasesxe2x80x9d, J. of Chromatography, 122, (1976) 3-16, studied reaction conditions to control the length of the bonded molecules and the effect of the length on absorption properties.
The present invention provides the use of functionalized oxide (e.g., silica, alumina, CeO) particles as abrasive particles in chemical mechanical polishing.
This has the advantages including abrasive particles which do not readily degrade in high pH slurries. In addition, the surface properties can be modified as needed to enhance selectivity by controlling, for example, the attraction/repulsion forces between the abrasive particles and the surface of interest.